Workshop on Hard Copy Line Graphics
Workshop on hard-copy line graphics at Carnegie Mellon University
Reddy, R., "Workshop on Hard Copy Line Graphics", RFC 320, DOI 10.17487/RFC0320, March 1972, <https://www.rfc-editor.org/info/rfc320>.
@misc{rfc320,
series = {Request for Comments},
number = 320,
howpublished = {RFC 320},
publisher = {RFC Editor},
doi = {10.17487/RFC0320},
url = {https://www.rfc-editor.org/info/rfc320},
author = {R. Reddy},
title = {{Workshop on Hard Copy Line Graphics}},
pagetotal = 3,
year = 1972,
month = mar,
} RFC text
Network Working Group R. Reddy
Request for Comments: 320 CMU
NIC: 9350 27 March 1972
Workshop on Hard Copy Line Graphics
At CMU we have recently interfaced a Xerox Graphic Printer (ex-LDX)
to the PDP-10 using a PDP-11 as in intelligent controller for the
printer. Specially designed interface and data structures permit the
PDP-11 to generate each scan line as needed without having to resort
to the brute force generation of the bit image for the whole page.
The attached pages were produced using this system with the help of a
document generation program and a character set design program. This
is something personal.
In response to several requests, we are conducting a one day workshop
on the XCRIBL system. The workshop will be held in 3124 Science Hall
at Carnegie-Mellon University on April 12. An agenda for the
workshop is attached. If you are interested in coming or sending
someone to this workshop, please contact Dr. D. R. Reddy (412-621-
6200 ext. 149), Mr. Mack Hicks (412-687-5846) or Miss M. Kostkas
(412-626-2600 ext. 141), for further information or local
arrangements. Local reservations may be made at the Webster Hall
Hotel (412-621-7700) or the Civic Center Motor Hotel (412-683-6700)
which are within walking distance of Carnegie-Mellon University.
CARNEGIE-MELLON UNIVERSITY
WORKSHOP ON HARD COPY LINE GRAPHICS
April 12
Morning
Document Generating Languages and Systems
9:00-9:30 Raj Reddy Overview of the XCRIBL system
9:30-10:20 Joe Newcomer Languages for Document Generation
10:20-10:30 Coffee Break
10:30-12:00 Examples of Document Generation
Letter Producing Systems
Technical Report Production
A Graphics and Gray Scale Image System
Afternoon
Systems Support
12:00-1:45 Lunch Character Sets (Generation and
1:45-2:45 Lee Erman Modification)
2:45-3:00 Coffee Break
3:00-4:00 George Robertson The PDP-11 Support System
4:00-5:00 Bill Broadly and The PDP-11 XGP Interface (Hardware)
Jack Wright
Evening
Session for the "Hackers"
7:30-10:30 Discussion session of as yet unsolved issues and
possible hardware-software solutions.
XCRIBL SYSTEM
COMPUTER SCIENCE DEPARTMENT
CARNEGIE-MELLON UNIVERSITY
What you are now reading is a computer printout produced by the
XCRIBL system. Computers printers do not have typefaces like this
one nor can they change typefaces. Conventional computer printers
cannot print character sets where the center to center distances are
not all the same. The machine that printed this document is a
facsimile copying machine built by Xerox a number of years ago. The
computer science department of Carnegie-Mellon University has
designed and constructed the interface to connect it to a
minicomputer (PDP-11) which in turn is linked to a large computer,
the PDP-10. The equipment has been working since January.
The Xerox Graphic Printer (XGP) works in a similar fashion to the
Xerox office copiers. Instead of reflecting light off a printed page
as in a copier the XGP uses a cathode ray tube similar to old
television tubes as a source of light. The image is drawn as a
series of dots on the CRT with a resolution of 12 dots per inch. The
line of dots is reflected onto a selenium drum which
electrostatically attracts a fine black powder to the exposed
selenium areas. The powder is transfered to a moving sheet of paper.
Finally a fuser melts the powder onto the paper.
To be able to print any character the pattern of dots which will be
printed as that character must be entered into the computer along
with an indicator of what the pattern represents. To facilitate this
a program has been written to design character sets. This program
draws a grid on a display terminal. Each box in the grid represents
one dot in the final Xerox output. The dots may be set or unset and
the character redrawn on the display as frequently as one might
desire. Because of the ease with which this may be done it becomes
an enjoyable task to design a character set and then be able to
change any part of any character.
The XGP is also capable of drawing lines and gray scale images. The
AI group is using the XGP to print pictures of faces and speech
spectrograms. The range of possible uses is boundless.
[This RFC was put into machine readable form for entry]
[into the online RFC archives by Helene Morin, Via Genie 10/99]
AI ELI5
On this page
§1The Xerox Graphic Printer Interface
Carnegie Mellon's Computer Science Department built an interface between its PDP-10 computer and a Xerox Graphic Printer (XGP) (a modified facsimile copying machine), using a PDP-11 as an intelligent controller. The XGP works like a photocopier but uses a cathode ray tube similar to a television as the light source instead of reflected light. The system has been working since January 1972.
A computer controls a special Xerox machine that can draw anything, not just type regular letters.
§2How the XCRIBL System Works
The XCRIBL system draws an image as a series of dots on the CRT with a resolution of 12 dots per inch. These dots are reflected onto a selenium drum, which electrostatically attracts a fine black powder to the exposed areas. The powder is transferred to moving paper and fused in place by heat. Instead of requiring the computer to generate a complete bit image of the entire page in memory, the system generates each scan line as needed, using special data structures and a character set design program that lets operators easily design and modify character sets in a grid on a display terminal.
The system draws dots in rows on a special drum, which then prints them on paper. You can design your own letters by editing them on a screen.
§3Capabilities and the April 12 Workshop
The XGP can print documents with any typeface, not the fixed fonts of ordinary printers. It can also draw lines and gray-scale images—the AI group used it to print pictures of faces and speech spectrograms. CMU held a one-day workshop on April 12, 1972 at Carnegie Mellon to teach other sites how to use XCRIBL. The morning covered document generation languages and systems; the afternoon covered character set generation, the PDP-11 support system, and hardware interface details. Evening sessions were reserved for open discussion of unsolved problems. Attendees could stay at the Webster Hall Hotel or Civic Center Motor Hotel, within walking distance of the university.
The system can print fancy letters and pictures. CMU offered a day-long class on how to use it, with time to ask questions in the evening.